Abstract: Background and purpose: Middle rectal cancer has higher local recurrence rate and metachronous distant metastasis rate after radical resection. If the high-risk populations of local recurrence and metachronous distant metastasis can be selected before the operation, the targeted treatment can be carried out for the high-risk groups, so as to improve the prognosis of patients. Our retrospective study was aimed to analyze the value of preoperative magnetic resonance imagine (MRI) in predicting postoperative recurrence and metachronous distant metastasis of middle rectal cancer. Methods: We retrospectively analyzed preoperative MRI and follow-up data of 278 patients with middle rectal cancer confirmed by histopathology at our hospital from March 2013 to December 2014. The correlations of MRI features with postoperative recurrence and metachronous distant metastasis were evaluated. The risk factors for postoperative recurrence and metachronous distant metastasis were analyzed. Results: Among 278 patients, 19 patients (6.83%) were confirmed to have postoperative recurrence and 42 patients (15.11%) were confirmed to have metachronous distant metastasis. There were 4 patients who had postoperative recurrence and metachronous distant metastasis at the same time. The mrT staging and peritoneal reflection invasion were significantly correlated with postoperative recurrence (P<0.001). And mrT staging (P=0.013), mrN staging (P<0.001), extramural vascular invasion (EMVI) (P<0.001) and peritoneal reflection invasion (P<0.001) were significantly correlated with metachronous distant metastasis in univariate analysis. Stepwise regression analysis showed peritoneal reflection invasion was a significant risk factor for postoperative recurrence (P<0.001). Both the mrN1 staging (P=0.017) and mrN2 staging (P<0.001) were significant risk factors for metachronous distant metastasis. Conclusion: Preoperative MRI of rectal cancer can provide better prediction of postoperative recurrence and metachronous distant metastasis. Thus, it is helpful in clinical screening of high-risk patients and individualized treatment to improve prognosis.

Key words: Middle rectal cancer, Magnetic resonance imaging, Local recurrence, Distant recurrence